Recently, a white light-emitting diode where a blue light-emitting element using a nitride-based compound semiconductor is utilized as the light emission source is being developed and studied, and since this is a lightweight, mercury-free and long-life device, demands therefor are expected to expand in the future. In a currently most common white light-emitting diode device, as described, for example, in Patent Document 1, a coating layer containing a fluorescent material capable of emitting yellow light by absorbing a part of blue light, and a mold layer for mixing blue light from the light source with yellow light from the coating layer are provided on the entire surface of a light-emitting element capable of emitting blue light, and a pseudo-white color is obtained by mixing blue and yellow colors which are in the complementary color relationship. As the coating layer, a mixture powder of cerium-activated YAG (Y3Al5O12:Ce) powder and epoxy resin has been conventionally employed. However, in this method, when applying the coating layer, for example, distribution unevenness of the contained fluorescent material powder or fluctuation in the amount of the fluorescent material powder among light-emitting diode individuals may occur and in turn, the light-emitting diode suffers from color unevenness.
In order to avoid such a problem, in Patent Document 2, a white light-emitting diode device obtained by forming a blue diode element having a light-emitting layer composed of InGaN on a substrate with the principal surface being the Al2O3 (0001) plane of a material having a texture where Al2O3 and Y3Al5O12:Ce are continuously and three-dimensionally entangled, has been reported. In the white light emitting diode device of this report, a method of causing blue light emitted from the light-emitting layer to be incident directly on the substrate, allowing transmission of the blue light in the Al2O3 phase, and emitting homogeneous yellow light in the Y3Al5O12:Ce phase, thereby efficiently extracting light only by a light-emitting chip without use of a fluorescent material powder-containing coating layer and obtaining homogeneous white light free from color unevenness, has been proposed.